Cytokines play an important role in regulating HIV-1 replication in lymphocytes and macrophages, and have therapeutic potential for AIDS. We have been investigating the impact of cytokines on HIV replication in macrophages and T cells and have studied the molecular mechanisms involved in their action. Interleukin(IL)-12 induces initiation of the differentiation of naive CD4+ T lymphocytes into T helper type 1 (Th1) cells and is important for the control of cell-mediated immunity. The specific receptor, CCR5, for the beta-chemokines MIP-1alpha, MIP-1beta, and RANTES functions as the primary coreceptor for macrophage-tropic isolates of HIV-1. We have discovered that IL-12, but not IL-4, IL-10, or IL-13, potently downmodulates the surface expression of CCR5 induced by IL-2 on both CD4+ and CD8+ T lymphocytes. Decreased CCR5 surface expression was not secondary to transcriptional inhibition, given that CCR5 mRNA was enhanced in cells cultured in IL-12/IL-2 compared with IL-2 alone. The effect of IL-12 in downmodulation of CCR5 surface expression was shown to be mediated by soluble factors secreted from the T cells. Rapid and transient [Ca2+]i was induced in monocytes by IL-12 induced supernatants, which desensitized the response of monocytes to a later treatment with MIP-1alpha, but not SDF-1. Neutralization with specific antibodies identified these factors as MIP-1beta and MIP-1alpha. IL-4, IL-10, IFNgamma and IL-18 primarily inhibited MIP-1beta secretion, and also weakly suppressed MIP-1alpha secretion. HIV-1 replication was inhibited in IL-2/IL-12 containing cultures, which correlated with chemokine and chemokine receptor levels. These data suggest that effects of IL-12 on beta-chemokine production and chemokine receptor expression may contribute to the immunomodulatory activities of IL-12 and have potential therapeutic relevance in controlling HIV-1 replication. HIV-1 replication involves multiple biochemical steps beginning with virus binding and entry, followed by reverse transcription, integration, transcription and then assembly and release of the virus particles. We have been studying a novel cell surface amino-acid transporter which when cross-linked on the cell surface with monoclonal antibodies leads to dramatic inhibition of HIV-1 replication. We have found that antibody binding elicits a tyrosine phosphorylation cascade that inhibits late stages of reverse trascription. Antibody triggering does not block virus binding, membrane fusion, or transcription following integration. The results suggest that non-immunologic pathways exist that regulate virus replication at post-entry steps. These studies provide a scientific foundation for a possible new therapeutic target for the treatment and prevention of HIV-1 infection.